1. Field of the Invention
The invention relates to devices and a method for removing a broken pulp web from a pulp dryer and to a maintenance platform for a pulp dryer.
2. Description of the Related Art
In a pulp dryer, a web formed of pulp, i.e. the pulp web, is conveyed along a multi-layered path by floating it on an air mattress formed by blowing nozzles. The blowing nozzles are arranged in several superimposed, generally horizontal nozzle levels almost having the length of the pulp dryer. The pulp web is typically introduced in the pulp dryer through its first end. Then the pulp web is conveyed along the uppermost nozzle level of the pulp dryer to the second end of the apparatus. At its ends, the apparatus typically comprises turn rolls, over which the pulp web is turned each time to the next lower nozzle level. When the pulp web has been conveyed to the lowermost nozzle level of the pulp dryer, the pulp web is removed from the pulp dryer, typically through the second end of the pulp dryer. A pulp dryer typically comprises 15 to 30 nozzle levels. The gas blown from the blowing nozzles typically consists of hot air, the blow air generally having a temperature in the range of 120° C. to 170° C. When reaching the pulp dryer, the pulp web typically has a dry solids content of 48% to 54%. The dry solids content of the pulp web leaving the pulp dryer is typically 85% to 95%, usually approximately 90%. The pulp web typically has a width of 3 m. to 9 m. The pulp web is typically conveyed at a speed of 140 to 220 m./min. in the pulp dryer.
The pulp web may break within the dryer for various reasons. In such a situation, the feed of new pulp web into the pulp dryer is interrupted. However, in the case of a web break, there will typically still remain a large amount of pulp web in the pulp dryer, and this web should be removed from the apparatus before the production is restarted.
In the case of a web break, the pulp web is currently removed from the dryer by means of extraction devices fixed to maintenance platforms moving vertically at the first and the second end of the pulp dryer. The extraction device comprises two horizontal rolls transverse to the direction of movement of the pulp web. The rolls are disposed opposite each other so that the nip of the extraction device is formed between them. The rolls are adapted to be rotated by machine force. The pulp web needs to be pulled by muscular force from within the dryer to the nip of the extraction device, and then the pulp web can be extracted by machine force with the aid of the rolls and further guided to a pulper. The distance over which the pulp web needs to be transferred by manpower is typically 2 to 3 meters. After a web break, the wet pulp web remains on the nozzle levels and will have time to dry before cleaning operations are started. Consequently, friction between the nozzle levels and the web will impede cleaning operations, even though nozzle blowing may make the situation somewhat easier. Extraction of the pulp web from the pulp dryer requires strong force. The operation usually requires 2 or 3 operators.
International Patent Application WO 02/101143 discloses a solution, in which a manually moved roll is used for pressing the broken pulp web by manpower against a rotating turn roll. In this manner, a pulling nip is formed between the roll and the turn roll, due to which the pulp web will start moving. This solution also calls for human force. The device of this solution also requires installation work to be done in the inner parts of the pulp dryer.